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1.
Intraseasonal oscillation of the rainfall variability over Rwanda and evaluation of its subseasonal forecasting skill 下载免费PDF全文
非洲中东部地区的经济主要依靠自给农业支撑,该地区农业经济对降水的变化尤为敏感.本文以卢旺达为例,观测分析指出卢旺达的次季节降雨主要集中在10-25天;根据次季节尺度降水变率的单点相关方法,发现卢旺达的次季节降水变率和周围区域变化一致;进一步合成结果显示该地区次季节降水变率与异常西风有关,这可追溯到赤道地区西传的赤道Rossby波.最后,本文评估了当前动力模式ECMWF对 卢旺达地区(即非洲中东部)次季节降水变率的预报能力,发现EC模式在对该区域降水和相关风场指数的预报技巧都在18天左右,且预报技巧表现出一定的年际差异,这可能与热带太平洋的背景海温信号有关.该工作增进了当 前对非洲中东部地区的次季节降水变率和预测水平的认知,并且对该地区国家粮食安全和防灾减灾具有启示性意义. 相似文献
2.
Isabelle McMartin Pierre-Marc Godbout Janet E. Campbell Tommy Tremblay Pouran Behnia 《Boreas: An International Journal of Quaternary Research》2021,50(1):51-75
A new digital map of glacial geomorphic features and interpreted glacial landsystems was produced for an area covering ~415 000 km2 in the Keewatin Sector of the Laurentide Ice Sheet (LIS) in Nunavut. The map integrates information from previous surficial geology maps and >14 000 field stations, and is significantly improved by the detailed inventory of ~152 000 glacigenic features using high-resolution ArcticDEM data and Landsat 8 imagery. From this, we identify and map coherent patterns of landform development (landsystems) between the Manitoba border and the Arctic coast, many of which are entirely new and others that are significantly modified or updated. In particular, we recognize six separate ice streams, including one probable remnant ice stream, and we delineate numerous palimpsest streamlined landscapes with associated ice-flow trends and relative ages. A continuum of relict terrains with varying basal ice thermal conditions is mapped for the first time in the ice divide migration zone between Baker Lake and Wager Bay. In addition, deglacial cold-based retreat terrains and preserved warm-based landscapes unaffected by younger glacial events have been identified. These new georeferenced, multi-scale data sets and interpreted glacial landsystems provide a comprehensive framework to strengthen reconstructions of the glacial history and dynamics of one of the largest ice domes of the LIS, identify distinct glacial sediment transport paths for applications to mineral exploration, and test numerical modelling of the LIS in support of climate change studies and long-term evolution of modern ice sheets. 相似文献
3.
Rhys G. O. Timms Ashley M. Abrook Ian P. Matthews Christopher P. Francis Agnieszka Mroczkowska Ian Candy Stephen J. Brooks Alice M. Milner Adrian P. Palmer 《第四纪科学杂志》2021,36(3):339-359
The influence of the North Atlantic on the margins of Europe means the region is particularly sensitive to changes in the ocean–atmospheric system. During the Last Glacial–Interglacial Transition (16–8 cal ka bp ) this system was repeatedly disrupted, leading to a series of abrupt and short-lived shifts in climate. Despite much research, the number and magnitude of these ‘centennial-scale’ events is not well understood. To address this, we expand upon investigations at Quoyloo Meadow, Orkney, Scotland, one of the best chronologically constrained palaeoclimate records in northern Britain. By coupling stable isotope and chironomid fossil analyses with existing data, this study identifies multiple phases of centennial-scale disturbance at: c. 14.0, 11.1, 10.8, 10.5, 10.45 and 10.3 cal ka bp , with the events at 14.0 and 10.3 exhibiting a particularly pronounced cold-climate signature. During the Holocene, the strongest response to climate forcing was at c. 10.3–10.0 cal ka bp , expressed as a two-stage drop in mean July temperatures, a shift in pollen spectra indicative of ‘less-stable’ climatic regimes, and a depletion in δ18O values. We interpret this as the first reliably dated incidence of the ‘10.3-ka event’ in the British Isles and consider the wider impact of this climatic reversal in other Holocene records. 相似文献
4.
Kaj Sullivan Daniel Layton‐Matthews Matthew Leybourne James Kidder Zoltn Mester Lu Yang 《Geostandards and Geoanalytical Research》2020,44(2):349-362
The characterisation of relative copper isotope amount ratios (δ65Cu) helps constrain a variety of geochemical processes occurring in the geosphere, biosphere and hydrosphere. The accurate and precise determination of δ65Cu in matrix reference materials is crucial in the effort to validate measurement methods. With the goal of expanding the number and variety of available geological and biological materials, we have characterised the δ65Cu values of ten reference materials by MC‐ICP‐MS using C‐SSBIN model for mass bias correction. SGR‐1b (Green River shale), DOLT‐5 (dogfish liver), DORM‐4 (fish protein), TORT‐3 (lobster hepatopancreas), MESS‐4 (marine sediment) and PACS‐3 (marine sediment) have for the first time been characterised for δ65Cu. Additionally, four reference materials (with published δ65Cu values) have been characterised: BHVO‐1 (Hawaiian basalt), BIR‐1 (Icelandic basalt), W‐2a (diabase) and Seronorm? Trace Elements Serum L‐1 (human serum). The reference materials measured in this study possess complex and varied matrices with copper mass fractions ranging from 1.2 µg g?1 to 497 µg g?1 and δ65Cu values ranging from ?0.20‰ to 0.52‰ with a mean expanded uncertainty of ± 0.07‰ (U, k = 2), covering much of the natural copper isotope variability observed in the environment. 相似文献
5.
Intensification of Southern Hemisphere westerly winds 2000–1000 years ago: evidence from the subantarctic Campbell and Auckland Islands (52–50°S) 下载免费PDF全文
6.
Birger Rasmussen Ian R. Fletcher Janet R. Muhling 《Contributions to Mineralogy and Petrology》2011,162(6):1259-1277
Xenotime is a widespread accessory mineral in lower greenschist to upper amphibolite facies metasedimentary rocks from the
Palaeoproterozoic Mount Barren Group, southwestern Australia. Xenotime is closely associated with detrital zircon, commonly
forming syntaxial outgrowths, in samples of sandstone, micaceous quartzite, slate, phyllite, garnet-bearing semi-pelites,
and in kyanite-, garnet-, and staurolite-bearing mica schists. In situ geochronology of xenotime from lower greenschist sandstones
has previously yielded multiple U–Pb ages with peaks at ~2.0, ~1.7, and ~1.65 Ga, interpreted to represent the age of detritus,
early diagenesis, and a later thermal event, respectively. New U–Pb dating of xenotime in slate yields a major population
at ~1.7 Ga with a minor population at ~1.2 Ga, reflecting diagenetic and metamorphic growth, respectively, whereas xenotime
in phyllite forms a minor age population at ~1.7 Ga and a main peak at ~1.2 Ga. Mid-greenschist facies semi-pelitic schists
(quartz-muscovite-garnet) contain xenotime that formed before 1.8 Ga and at 1.2 Ga, representing detrital and peak metamorphic
ages, respectively. Xenotime in samples of amphibolite facies schist (650°C and ~8 kbars) yields U–Pb ages of ~1.2 Ga, coinciding
with the time of peak metamorphism. A single analysis of a xenotime core from an amphibolite facies schist gave an age of
~1.8 Ga, consistent with the presence of detrital xenotime. Our results suggest that detrital xenotime may be preserved under
greenschist facies conditions, but is largely replaced during upper amphibolite facies conditions. Detrital xenotime is replaced
through dissolution–reprecipitation reactions forming compositionally distinct rims during greenschist and amphibolite facies
metamorphism at 1.2 Ga. Diagenetic xenotime is present in lower greenschist facies samples, but was not observed in metasedimentary
rocks that had experienced temperatures above mid-greenschist facies metamorphism (450°C). The apparent disappearance of detrital
and diagenetic xenotime and appearance of metamorphic xenotime during prograde metamorphism indicates that some of the yttrium,
heavy rare earth elements, and phosphorus needed for metamorphic xenotime growth are probably derived from the replacement
of detrital and diagenetic xenotime. 相似文献
7.
Atlantic croaker is one of the most abundant demersal fish in Chesapeake Bay. Until recently, when substantial declines in
abundance have occurred, high biomass supported elevated fisheries landings. Therefore, study of the diet of Atlantic croaker
is important to understand its own dynamics and its role in the Chesapeake Bay ecosystem. Patterns in the diet of croaker
varied annually, seasonally, and spatially, but were not strongly correlated with any measured environmental variables. Although
the majority of the diet of croaker consisted of polychaetes and other benthic items, about 20% of the croaker diet by weight
consisted of anchovy and other fishes. Croaker consumption of anchovy is likely a result of crepuscular feeding that has not
been captured in previous studies that sampled during the day and with bottom trawls. Thus, croaker influences both the benthic
and pelagic components of the Chesapeake Bay food web and incorporating such diel patterns in diet may increase the reliability
of fishery ecosystem models. 相似文献
8.
Kathryn A. Matthews Michael T. Murrell Steven J. Goldstein Andrew J. Nunn Deborah E. Norman 《Geostandards and Geoanalytical Research》2011,35(2):227-234
Here we report uranium and thorium isotopic ratios and elemental concentrations measured in solid reference materials from the USGS (BHVO‐2G, BCR‐2G, NKT‐1G), as well as those from the MPI‐DING series (T1‐G, ATHO‐G). Specifically created for microanalysis, these naturally‐sourced glasses were fused from rock powders. They cover a range of compositions, elemental concentrations and expected isotopic ratios. The U‐Th isotopic ratios of two powdered source materials (BCR‐2, BHVO‐2) were also characterised. These new measurements via multi‐collector thermal ionisation mass spectrometry and multi‐collector inductively coupled plasma‐mass spectrometry can now be used to assess the relative performance of techniques and facilitate comparison of U‐Th data amongst laboratories in the geoscience community for in situ and bulk analyses. 相似文献
9.
10.
The current study focuses on understanding key factors controlling geochemical export in eight diverse coastal watersheds at seasonal and annual time scales. Geochemical, atmospheric and hydrologic data across a range of hydro‐climatic regimes and varying land uses were investigated and relationships analysed. A hyperbolic dilution model was fitted for each watershed system to evaluate discharge–concentration relationships. Nitrate concentration effects were observed in watersheds exposed to high atmospheric deposition rates as well as agricultural watersheds, whereas urban watersheds showed nitrate dilution effects. Dilution patterns were observed for calcium, magnesium and sulfate for almost all watersheds. Seasonal loads for almost all constituents were noted to be mainly driven by hydrologic seasonality, but are also dependent on inputs (atmospheric deposition and land use sources). Understanding the primary controls on hydro‐chemical interactions is critical for developing and refining predictive water quality models, especially in coastal watersheds where sensitive downstream ecosystems act as receiving waters for upstream pollutant loads. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献